Objective: The purpose of the study is to identify effective and ineffective critical behaviors on the part of nurses and psychiatric aides in giving care to the mentally ill. The product of the study will be two source books of critical nursing behaviors, one for nurses and one for psychiatric aides. These books are intended for use in developing materials for training, selection, performance evaluation, criterion research, or other types of research. Method: Critical incidents of effective and ineffective behavior will be collected about nurses and aides, from nurses and aides, in 36 mental health facilities, including psychiatric hospitals, general hospitals offering psychiatric services and community mental health centers. Four major geographic areas will be sampled. The incidents will be classified inductively into behavioral categories. Each incident will be abstracted into a one or two-line summary; these abstracts will be reported in the source books under their appropriate behavioral categories. The source books also will include suggestions for use of the material and instructions for preparing rationales for the intended use.